． How to deal with dyeing defects such as uneven streaks and too dark colors after dyeing with vat dyes?
Answer: After the spun yarn or fabric is colored with vat dyes, dyeing defects are generally difficult to remove. Here are several color stripping methods for reference.
Method 1: 23.5% (30°Bé) NaOH 20~25mL/L, insurance powder 5~6g/L, polyvinylpyrrolinone 3mL/L, magnesium sulfate 10g/L, liquor ratio 1: (20~ 40), temperature 80~100℃, treatment for 30 minutes.
Method 2: 1.5% water softener (based on fabric weight), dispersant 2~3g/L, 30% (36°Bé) NaOH 10~15mL/L. Insurance powder 5g/L, sodium nitrite (only Suitable for vat dyes that are prone to over-reduction) 1g/L, polyvinylpyrrolinone 2~3mL/L. Use indirect steam to heat to 75~80°C and treat for 30 minutes. After the treatment is completed, use 1mL/L 30% (36°Bé) NaOH, 1g/L insurance powder, 1g/L dispersant mixture, clean at room temperature for 5 minutes, and then Rinse with running water, and if necessary, use 1 to 2 mL/L 35% hydrogen peroxide at 55°C. This method is suitable for color stripping processing in rope coloring machines.
Method 3: 30% (36°Bé) NaOH 10~12mL/L, insurance powder 5~6g/L, polyvinylpyrrolinone 3mL/L, dispersant 5g/L, liquor ratio 1:5 (light color), 1:10 (medium color), 1:20 (dark color), 90~95℃ in four passes in the jigger. First add caustic soda and dispersant, raise the temperature to 90-95°C, stop heating, and add insurance powder and polyvinyl pyrrolinone.
Method 4: 3 parts sodium lignosulfonate, 1 part magnesium sulfate. In every 4.546L caustic soda and insurance powder mixture, add 1/8 to 4/5 0·0284L or more of the mixture to perform stripping treatment. Various colored materials can be stripped using the above method. After stripping and then re-coloring (same coloring prescription), the stripping effect should be determined by the nature of the dye. The above stripping methods only partially strip the color. If you want to completely strip the color, you need to repeat the stripping process to meet the requirements.
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